Interpretive Summary: Coastal bermudagrass can be grown as an alternative energy resource (bioenergy crops) using treated swine wastewater distributed through a subsurface drip irrigation system. Using treated effluent for bioenergy crop production purposes allows the crops to be irrigated without overloading the crops with nutrients. At one experimental site, we examined the influence of subsurface drip irrigation that applied treated swine wastewater and commercial fertilizer below the soil surface on both the quantity and quality of bermudagrass bio-energy. Bermudagrass irrigated with commercial fertilizer had slightly greater energy per kilogram. However, bermudagrass irrigated with treated swine wastewater produced more hay. This increase in hay production directly contributed to as much as a quarter percent increase in energy per hector. Irrigation with treated swine wastewater yielded greater concentrations of certain minerals that are known to positively influence downstream, high-temperature, conversion processes by promoting less solid by-product and greater combustible gas formation.

Technical Abstract:
Coastal bermudagrass (Cynodon dactylon L.) may be a potentially important source of bio-based energy in the southern United States due to its vast acreage. It is often produced as part of a waste management plan with varying nutrient composition and energy characteristics on fields irrigated with livestock wastewater. The objective of this study was to determine the effect of subsurface drip irrigation with treated swine wastewater on both the quantity and quality of bermudagrass bio-energy. The treated wastewater was recycled from an advanced treatment system and used for irrigation of bermudagrass in two crop seasons. The experiment had nine water and drip line spacing treatments arrayed in a randomized complete block-design with four replicates. The bermudagrass was analyzed for calorific and mineral contents. Bermudagrass energy yields for 2004 and 2005 ranged from 127.4 to 251.4 Gigajoules per hectare. Compared to irrigation with commercial nitrogen fertilizer, the least biomass energy density was associated with bermudagrass receiving treated swine wastewater. Yet, in 2004 the wastewater irrigated bermudagrass had greater hay yields leading to greater energy yield per hectare. This decrease in energy density of wastewater irrigated bermudagrass was associated with increased concentrations of potassium, calcium, and sodium. After thermal conversion, these compounds are known to remain in the ash portion thereby decreasing the energy density. Nonetheless, the loss of energy density using treated effluent via subsurface drip irrigation may be offset by the positive influence of these three elements for their catalytic properties in downstream thermochemical conversion processes such as carbonization and gasification processes promoting a lesser char yield and greater combustible gas formation.